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Tectonics > 1.3 > Flashcards

1.3 Flashcards

1
Q

Focus

A

Origin of the earthquake in the crust.

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2
Q

Epicentre

A

Above the focus on the earth’s surface.

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3
Q

Seismograph

A

What earthquakes are recorded on.

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4
Q

Body waves

A

P waves, S waves

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5
Q

Surface waves

A

Love waves, Rayleigh waves

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6
Q

P waves

A

Fastest to travel, back and forth motion, travels through solids and liquids.

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7
Q

S waves

A

60% slower than P waves, up and down motion, travels through solids only.

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8
Q

Love waves

A

Surface wave, travels through solids only, side to side motion.

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9
Q

Rayleigh waves

A

Surface waves, travels through solids only, elliptical motion, responsible for most of the shaking felt by people. Spreads furthest from the epicentre.

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10
Q

Primary effects of seismic waves

A

ground shaking, crustal fracturing

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11
Q

Secondary effects of seismic waves

A

Liquefaction - rocks loose strength due to violent shaking and become more liquid than solid.
Landslides and avalanches.
Tsunamis - water above displaced.

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12
Q

Key dates of Christchurch 2011

A

Six earthquakes from 04/09/10 to 23/12/11 from magnitude 5.3 to 7.1.
Feb 22nd 2011 only one causing casualties.

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13
Q

Geological and ground conditions of Christchurch

A

Deep alluvial soils (fine soils) of Canterbury Plains. The area was originally a swamp = sand and silt (soft wet sediment). Shallow soils only 10m thick in some areas, maximum of 40m.
Shallow water table - 5m deep in Western suburbs.

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14
Q

Factors increasing risk in Christchurch

A

Developed country = high repair cost for damages.
Alluvial soils
Abundance of water systems
Flooding river
Densely populated
Multiple earthquakes in a short period of time.

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15
Q

Impacts of liquefaction in Christchurch

A

Extensive damage to properties, lifelines, and infrastructure.
Large volume of sand and silt covering buildings.
Mud and water flooding streets.
Permanent tilt of houses, foundations and structural damages.
Damage to buried pipe networks.
20,000 residential buildings severely affected.
8,000 residential buildings damaged beyond repair.

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16
Q

Key dates of Kashmir 2005

A

October 8th 2005 = magnitude 7.6 earthquake triggering several thousand landslides.
Epicentre near Muzaffarabad, Pakistan.
30-40km from airport.

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17
Q

Factors increasing risk in Kashmir

A

Geology - silt, sandstone, clay, and mudstone. Easily eroded and not condensed, prone to landslides.
Weak rock type.
Shear valleys
Proximity to settlements
Proximity to water sources
Remote location - aid response time.
Level of development.
Steep relief

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18
Q

Impacts of landslides in Kashmir

A

Flooding endangered residents in Hattian village (2.8km downstream).
Damage to bridges
Destroyed houses at or near stream level.

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19
Q

Mitigation techniques to minimise impacts in the future.

A

Flood routing models appropriate to conditions of landslides deposits with an excavated spillway.
Data and construction with field engineers so information can be transferred to people preparing digital evaluation models and other critical data for the landslide dam-breach analysis.

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20
Q

Characteristics of Basaltic lava

A

Low viscosity
Low silica content
Gas escapes
0.5-2% gas
Divergent plate margin
1000-1200 degrees
High eruption frequency
Gentle, effusive eruptions
Shield volcanoes
Low explosivity

21
Q

Characteristics of andesitic lava

A

Intermediate viscosity
Medium silica content
Traps gas
3-4% gas
Conservative plate margin
800-1000 degrees
Violent, moderate explosive eruptions
Composite volcanoes
Moderate explosivity

22
Q

Characteristics of rhyolitic lava

A

High viscosity
High silica content
Traps gas
4-6% gas
Conservative plate margin
650-800 degrees
Low eruption frequency
Very violent eruptions
Composite/stato volcano
High explosivity

23
Q

Jökulhlaups (secondary hazard)

A

Snow and ice in glaciers melt after an eruption which causes sudden floods that are very dangerous.

24
Q

Lava flows (primary hazard)

A

Streams of lava that have erupted onto the Earth’s surface. Fast flowing lava can be very dangerous depending on it’s viscosity and silica content.

25
Q

Pyroclastic flows (primary hazard)

A

A mixture of hot, dense rock, ash, lava, and gases which move very quickly along the Earth’s surface. They travel at high speeds, are very dangerous and can cause asphyxiation (lack of oxygen supply) for anyone caught in the flow.

26
Q

Tephra and ash flows (primary hazard)

A

Pieces of volcanic rock and ash blasted into the air causing damage to buildings, which can collapse under the weight and disruption to flight paths.

27
Q

Volcanic gases (primary hazard)

A

Gases like sulphur dioxide and carbon monoxide released into the atmosphere. can travel long distances due to their potency.

28
Q

Lahars (secondary hazard)

A

A combination of rock, mud, and water, which travel quickly down the sides of a volcano. Can occur during the heat of the eruption causing snow and ice to melt or when an eruption coincides with heavy rainfall.

29
Q

Acid rain (secondary hazard)

A

Gases such as sulphur dioxide are released into the atmosphere.

30
Q

Similarities between lahars and jökulhlaups

A

Travel at high speeds
Contain water and volcanic material
Pick up material and debris whilst travelling.

31
Q

Example of a jökulhlaup

A

Eyjafjallajökull 2010 - aah clouds disrupted aeroplanes, changed river channel routes.
Event was anticipated - main road closed and breaches made in road embankment to allow water and deposits to pass through with minimal damage.

32
Q

Example of pyroclastic flow

A

Chances Peak, Montserrat 1997 - destroyed capital town of Plymouth

33
Q

Example of flank fissure

A

Nyiragingo volcano, 1977 - lava bombs, flank fissure drained lava lake in under an hour. Swamped several villages killing many. Occurred at night = people asleep, unprepared, no evacuation.
Quick onset = velocity of 20-60km/hr for 9km.

34
Q

Flank fissure

A

The release of lava and pyroclastic material from a source on the slopes of a volcano instead of it’s primary central vent.

35
Q

Example of tephra

A

Eyjafjalljökull, 2010 - ash cloud present over trans-Atlantic flight path, disrupted aircraft movement for a week.
Local evacuations of 700 people.
Closure of main road due to poor visibility.

36
Q

Example of volcanic gas

A

Mount Pinatubo, 1991 - produced a 20 million ton sulphur dioxide cloud. 32km high and cooled the Earth for around 3 years by 0.6 degrees.

37
Q

Tectonic setting of Iceland

A

North Atlantic Ridge, divergent plate margin (constructive). 30+ active volcanic systems, eruptions 3-5 years, many under ice caps.

38
Q

Key details of Eyjafjallajökull eruption 2010

A

Moderately active ice-capped volcano, 18 years of intermittent volcanic unrest.
20th March to 12th April 2010 = effusive lava eruption
14th April to 22nd May 2010 = explosive summit eruption

39
Q

Management before the Icelandic 2010 eruption

A

Signs of renewed activity at the beginning of 2010 - authorities prepared for potential eruption.
Full scale evacuation tested in 2006 by the Icelandic department of Civil Protection and Emergency Management (ICP).

40
Q

Management during the Icelandic 2010 eruption.

A

Immediate activation of the ICP system (emergency phase) - highest priority activation orders and red cross emergency shelters set up.
Temporary service shelters for locals set up by ICP.
Farmers allowed to go into hazard zones for 2 hours to tend to livestock (created good relationship between locals and authority).
47% didn’t evacuate as they had livestock or elderly to look after.

41
Q

Impacts of the Icelandic eruption

A

Flood outburst = roads closed and access restrictions around eruption site.
Dense ash = difficulty seeing and breathing.
Ash cloud caused international flights to be stopped across Iceland and Europe.
No deaths, or injuries due to most residents evacuating when asked.

42
Q

Social impacts of Iceland 2010

A

Shift in European regulation and risk management.
Disrupted 10 million people.
Short term health problems from ash cloud = asthma, mental distress, anxiety amongst kids.
Long term health problems = skin rash, back pain, insomnia.
2 indirect deaths from hypothermia.

43
Q

Economic impacts from Iceland 2010

A

Disruption to aircraft (biggest since WW2) - worldwide loss of €3.75 billion.
Due to increased media exposure, Iceland’s tourism industry became their biggest economic contributor, growing 20% each year until 2020.

44
Q

Indian Ocean Tsunami 2004 - short term impacts

A

Social - Andaman and Nicobar cut off as jetties were destroyed. Some villages 70% killed, 50 million affected, 300,000 died.

45
Q

Indian Ocean Tsunami 2004 - mid term impacts

A

Environmental - most vegetation and topsoil removed up to 800m inland.

Economic - Sri Lanka had 60% of it’s fishing fleet and industrial infrastructure destroyed.

Social - Sumatra had 1,500 villages destroyed. Economies devastated and thousands lost their jobs.

46
Q

Indian Ocean Tsunami 2004 - long term impacts

A

Environmental - Fresh water supplies and agricultural soil contaminated by saltwater. Ecosystems (coral reefs, mangroves, forests, wetlands) severely damaged.

Economic - Thailand, tourism industry lost around $25 million a month and 120,000 workers lost their jobs.

Social - 1.7 million homeless.

47
Q

Indian Ocean Tsunami 2004

A

The deadliest tsunami recorded in history. Global volume of aid and relief provided to the affected developing countries was larger than ever before.

48
Q

How is a tsunami formed?

A

Usually caused be an underwater earthquake or volcanic eruptions. Tend to occur along plate boundaries.

A displacement of a large area of the seafloor causes a displacement of the water column above. Waves radiate from the source in all directions.

The nature of tsunami waves will depend on: the cause of the wave (earthquake or eruption), distance travelled from source (energy lost), water depth, offshore topography.

As water shallows, wave slow down and increase in height to produce onshore waves of up to 30m high.

Sea-floor irregularities reflect some wave energy so less reaches the coast.

Forth or fifth wave is usually the biggest wave, 40% of the wave energy is scattered back to sea and 60% is expended at or near the coast.

Death and destruction will depend on land uses, population density, and warning given.

49
Q
A

Tectonics (2 decks)

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